Crash on 15w43a server.

[22:43:05] [Server thread/INFO]: Starting minecraft server version 15w43a
[22:43:05] [Server thread/INFO]: Loading properties
[22:43:05] [Server thread/INFO]: Default game type: SURVIVAL
[22:43:05] [Server thread/INFO]: Generating keypair
[22:43:05] [Server thread/INFO]: Starting Minecraft server on ##.##.###.###:25605
[22:43:05] [Server thread/INFO]: Using default channel type
[22:43:05] [Server thread/INFO]: Preparing level "ss15w43a"
[22:43:06] [Server thread/INFO]: Preparing start region for level 0
[22:43:07] [Server thread/INFO]: Preparing spawn area: 6%
[22:43:08] [Server thread/INFO]: Preparing spawn area: 11%
[22:43:09] [Server thread/INFO]: Preparing spawn area: 20%
[22:43:10] [Server thread/INFO]: Preparing spawn area: 29%
[22:43:11] [Server thread/INFO]: Preparing spawn area: 39%
[22:43:12] [Server thread/INFO]: Preparing spawn area: 48%
[22:43:13] [Server thread/INFO]: Preparing spawn area: 56%
[22:43:14] [Server thread/INFO]: Preparing spawn area: 64%
[22:43:15] [Server thread/INFO]: Preparing spawn area: 76%
[22:43:16] [Server thread/INFO]: Preparing spawn area: 91%
[22:43:17] [Server thread/INFO]: Done (11.465s)! For help, type "help" or "?"
[22:43:39] [User Authenticator #1/INFO]: UUID of player deafgeek is 166b224a-da51-4510-ae42-50ead5bcb0cf
[22:43:40] [Server thread/INFO]: deafgeek[/#:56131] logged in with entity id 1224 at (-186.5, 66.0, 184.5)
[22:43:40] [Server thread/INFO]: deafgeek joined the game
[22:43:44] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 4114ms behind, skipping 82 tick(s)
[22:43:59] [Server thread/INFO]: [deafgeek: Given [Chest] * 1 to deafgeek]
[22:43:59] [Server thread/INFO]: deafgeek lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[22:43:59] [Server thread/INFO]: deafgeek left the game
[22:44:03] [User Authenticator #2/INFO]: UUID of player deafgeek is 166b224a-da51-4510-ae42-50ead5bcb0cf
[22:44:03] [Server thread/INFO]: deafgeek[/#:56157] logged in with entity id 3683 at (-188.231488806643, 67.0, 183.66686840124734)
[22:44:03] [Server thread/INFO]: deafgeek joined the game
[22:44:05] [Server thread/INFO]: deafgeek lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[22:44:05] [Server thread/INFO]: deafgeek left the game